This invention relates to the processing of articles that may contain cavities therein, and, more particularly, to the removing of bubbles from such cavities to permit processing of the interiors of the cavities.
During the manufacture of microelectronic devices, it is sometimes necessary to establish an electrically conductive path from a back side of a semiconductor wafer to a device structure on the front side of the wafer. One approach to producing such a conductive path is to form a small cavity or hole, termed a "via" in the art, through the wafer from the back side to the device structure on the front side. The interior of the via is electroplated with a layer of all electrically conductive material to form an annular conductive path or, alternatively, the entire volume of the via may be filled with a metallic conductor.
There are several techniques for forming the via through the wafer, such as patterning and wet etching, patterning and dry etching, laser etching, and the like. To electroplate an electrically conductive layer into the via, those parts of the wafer that are not to be electroplated are protected by a mask. The masked wafer is immersed into an electroplating solution. With the wafer made the cathode of an electroplating cell, ions of the conductive material are plated onto the walls of the vias from the electroplating solution.
If the vias are very small in diameter, air bubbles may remain in the vias when the wafer is immersed into the electroplating solution. The smaller the vias in diameter and the longer their lengths relative to their diameters, the more likely that bubbles remain in the vias after immersion. If the vias are blind holes that end in obstacles at their bottoms, as is often the case, it is even more difficult to remove the bubbles. For example, in a case wherein blind vias are about 10-30 micrometers in diameter and about 100 micrometers long, it is estimated from observation that as many as one-half of the vias retain air bubbles therein upon immersion into an acidic aqueous electroplating solution.
It is necessary to remove the bubbles from the vias prior to electroplating. If a bubble remains in a via, the electroplating solution never reaches the interior of the via, the via wall is not plated with a conductor, and the required conductive path from the back side to the front side of the wafer is never completed. The microelectronic device may consequently be inoperable.
There is a need for a highly reliable technique for removing bubbles from the interiors of vias and other types of cavities during processing. The approach must be operable for large numbers of vias of small diameters. The larger the diameter of the via, the easier it is to remove bubbles. On the other hand, the larger the diameter of the via, the less efficient is the space utilization of the microelectronic device.
The present invention fulfills the need for such a technique for removing bubbles from vias of small diameter, and further provides related advantages.